Dr. Kornman and colleagues’ reading list of highly cited and otherwise classic papers, which had shaped modern Periodontology, has been published by AAP’s Journal of Periodontology this month, and has been widely welcomed by likewise practitioners and undergraduate and postgraduate teachers. At the same time, scientists have noted time and again that frequent quotation does not mean high quality of a paper but often rather mainstream. I have discussed, in a previous post, several seminal papers in oral microbiology and risk assessment which were missing in Dr. Kornman’s list but which have had a considerable impact at the time when published. In their topic #3, Kornman et al.  point to the fact that,
3. Periodontal diseases encompass multiple conditions of the teeth-supporting tissues, including periodontitis which involves multiple entities with different etiologies, different clinical and biological characteristics, and different treatment needs
When discussing with colleagues the current classification system of periodontal diseases and conditions there is hardly anybody who won’t find the 1999 consensus as regards the differentiation between chronic and aggressive periodontitis anything else than awkward. The brief introductory remarks of the 1999 consensus workshop which has been published in a now dozed off AAP enterprise (Annals of Periodontology) by Armitage (1999)  has got an impressive 2,124 citations. Two of the three remaining highly cited papers had been listed also under the risk factor theme (#2) while the paper by Löe and Silness (1963)  has described a methodological issue and, no wonder, has therefore been cited 4,161 times. While two of the three consensus papers (derived from reading lists of several U.S. graduate programs) won’t exactly fit under the topic, the classic paper by Löe et al. (1986)  on natural history of periodontal disease in man (which seems to differ in different parts of the world) had been cited an impressive 609 times (as assessed on 27 January 2014). I am missing a bit the controversy which had emerged in the aftermath of the 1999 World Workshop on the classification of periodontal diseases and conditions. For instance the much clarifying paper by Baelum and Lopez (2003)  who point to the complete outdated conception of (re-)defining a syndrome (i.e., periodontitis) essentialistically (i.e., “as if it has an independent existence”). Although the paper has been quoted just 47 times it had made a huge intellectual impact. It certainly has (or should have) played a role in both undergraduate and postgraduate teaching. A couple of years later, Van der Velden (2005)  (quoted 47 times) in entertaining the inappropriateness of the “essentialistic” idea for classifying periodontitis, and favoring a nominalistic approach, quotes Scadding (1996),
“Essentialist definitions [of diseases] typically start ‘X is . . .’, implying a priori the existence of something that can be identified as X.
“The essentialist’s hankering after a unified concept of diseases as a class of agents causing illness, is mistaken and misleading for several good reasons: many diseases remain of unknown cause; known causes are of diverse types; causation may be complex, with interplay of several factors, intrinsic; and, more generally, an effect – the disease – should not be confused with its own ’cause’.” 
Flemmig (1999), in his paper on “Periodontitis” which had been prepared before and during the workshop (and has been quoted 247 times), had already then pointed to the pitfall of defining chronic and aggressive forms of periodontitis in an essentialistic way. As he wrote ,
“There is no scientific basis for the classification ‘adult periodontitis’ and ‘refractory adult periodontitis’. Extensive clinical examinations are required for the diagnosis of ‘rapidly progressive adult [sic!] periodontitis.’ It appears unrealistic that these examinations can be performed routinely in clinical practice.”
In his paper, Flemmig (1999) had attempted to clarify that extent and severity, as well as progression rate, of periodontitis are more or less normally distributed. So, it won’t make sense to define one tail of the distribution as an “aggressive” entity by its own.
Classification systems must not be amended every couple of years. The periodontal community has witnessed revisions in 1989 (a World Workshop organized by the AAP), in 1994 (by the European Federation of Periodontology) and again in 1999. The upcoming issue of Periodontology 2000 is dedicated once again to all aspects of “aggressive periodontitis” and acute periodontal conditions . It will appear, so we were promised, in April this year. Especially the Amsterdam group, around Drs. B. Loos and U. van der Velden, has called for a new workshop on classification for some time. It is hoped that a detailed dealing, in Perio 2000, with all aspects, be it clinical, immunological and microbiological, will increase pressure by the scientific community to organize a workshop including all critical minds. Eventually the concept of a sub-classification might be abandoned at all.
 Löe H, Anerud A, Boysen H, Morrison E. Natural history of periodontal disease in man. Rapid, moderate and no loss of attachment in Sri Lankan laborers 14 to 46 years of age. J Clin Periodontol 1986; 13: 431-445.
 Flemmig TF. Periodontitis. Ann Periodontol 1999; 4: 32-37. Note that the paper is called Periodontitis, not Adult, or Chronic Periodontitis. Flemmig’s obvious proposal to abandon any sub-classification and just talk about “periodontitis” had apparently been turned down by session chairs and organizers of the workshop (as a matter of fact, there has never been rapidly progressive “adult” periodontitis).
 The issue of Periodontol 2000 has been largely delayed after authors were given a deadline for preparing the reviews in summer 2012. Requests for updates especially on the systematically reviewed portions of the chapters were unfortunately turned down by the editor-in-chief in autumn 2013.
27 January 2014 @ 2:26 pm.
Last modified June 16, 2014.